The development of methods for high resolution two-dimensional gel electrophoresis and computer methods for quantitative analysis makes it possible to analyze gene expression in differentiated cells much more comprehensively than ever before. We now have the technology to measure the rates of synthesis of several thousand proteins from many different cell lines and animal tissues. We will use this technology to 1) analyze the patterns of protein synthesis in a broad spectrum of rat cell types, and 2) to analyze muscle cell differentiation in depth. The data obtained in these studies will be stored in the computer, in terms of a standard coordinate system, and we will use the computer to analyze this data in many different ways. We expect to gain insights into the ways that genes are controlled in sets during development, and we hope to find evidence for possible regulatory events during myogenesis. As we learn to interpret the complex patterns of protein synthesis, our collection of standardized data will become an increasingly valuable resource for ourselves and for others who wish to use it in the future.